I had over 22530 kms on it when I did the upgrade. As for which would work better I can't answer that, but I kept the stock springs and just used preload adjusters and they seem to work fine. As for fork oil, again I can't say because I just did it and I used Spectro. It surely wouldn't hurt to use Amsoil like they recommend. From what I read, Spectro and Amsoil were fairly similar except the Spectro is a blend. I did notice that there was a bit of gunk building up in the bottom of the forks so I plan on changing the oil about every 16k klm's. It's not that hard to do if you have a place to do it and the tools. I do recommend an air impact gun for removing the bolts holding the damping rods in... but not for putting them back in.